Good things come in threes. The number three has a lot of good connotations in many cultures, in fact, and there is something oddly satisfying about how perfectly events tend to work in that structure. Since this is a phenomenon that is colloquially reported on in real life, it makes sense that the rule of three would find its way into popular culture. Anime is no exception to this fact and this foundational idea is most readily found in the core protagonists of shonen anime.
Source：https://www.cbr.com/naruto-team-7-shonen-anime-freudian-trio-traits/
